Friday, October 15, 2004

Just how long do we have to wait for a quantum computer?

In the last five months we (humanity) have taken a few steps or flying leaps closer to a real quantum computer. Hogwash, poppycock you say. Bite thy tongue sir and let your ears (or eyes in this case) be thy judge.

It used to be that if (god knows why) one had the urge to measure a photon or group of photons one would use the time tested caveman method. That is crashing it into an “interference phenomena” like a spectrometer or homodyne detector resulting in the proton(s) being destroyed. Starting in June of this year a few physicists at the University of Queensland (of the land “downunder”) conceived of a measurement system that allows them to spy on individual photons. Meaning we can observe the universe on a quantum scale as we have never been able to do before. (note to other physics geeks.. not only that but they can observe BOTH the wave and particle qualities of the photon simultaneously.)

Also in June some physicists at the National Institute of Standards and Technology demonstrated the teleportation of atomic states (both spin state and phase) with no physical link. Being that it is difficult at best to move qubits efficiently, transportation of atomic states would allow a quantum computer to share and/or process information with much greater efficiency that current technology. To think I was content with transferring data over a wire or through a groove in silicon at the speed of light. In laymen’s terms, instant communication between different parts of a quantum computer. “But what of this qubit you speak sir” you say. Think bit, as in 1 or 0, but with the ability to also have any value in between, limited only by the accuracy of our measurement.

So you are a quantum physicist or mathematician and you have some theoretical quantum algorithms that you would like to test. Well dream no longer my friend, during the bountiful month of June, in an article brought to us by the informative people at Nature, the boys over at FIRST (Fraunhofer Institute for Computer Architecture and Software Technology) created the most powerful simulated quantum computer in existence. “Fat lot of good that does me!” you say. Well don’t get your panties in a wad quite yet, those nice chaps over at FIRST were also kind enough to make it available on-line. “AVAST! Those scoundrels are after me buried treasure.” you say. Well fear not good sir, because it is free as well. By now I am sure at least one person reading this will want to know the site. But this link in the original article was dead for me so you can check out the original article that is both on phyorg.com and on the FIRST website. The FIRST website also has contact information.

Back in July some of our fellow geeks out at UCLA were able to flip the spin of a single electron of a regular transistor chip. But more importantly they were able to measure the change in the spin. Not an easy task by any stretch of the imagination.

So that whole transportation of atomic states thing rubs you the wrong way. Think its just too damn complicated to be of any good in the near future. Well Professor Steven Girvin at Yale University may have the answer for you, circuit quantum electrodynamics. Specifically, the coherent coupling of a single photon to a Cooper pair box. Brain hurting right about now? They “couple a single photon to a single superconducting qubit (quantum bit or artificial ‘atom’).” “Arrrr, what be this artificial atom thingie?” you say. It is actually a chunk about a billion, that’s 9 zeros kids, aluminum atoms acting like/simulating/pretending to be a single atom. Then they take a microwave photon, which has a wavelength of about a centimeter, and trap it so it can be absorbed and emitted over and over again by the “atom”. (For the record the visible light spectrum is approximately 390 to 720 nm.) The photon is absorbed and regurgitated some where near the order of 12 million, that’s 6 zeros kids, times a second. This results in the “formation of a novel quantum state that is partly photon and partly atom excitation.”

Now I must take you back to Computer Science 101 for a moment. For those of you who know what a register is you can skim the first few sentences or just read it for a refresher. We all know that data on a computer is represented in the form of 1s and 0s known as a binary code. The CPU itself has a specialized high-speed memory that is commonly known as the register. This is actually incorrect, as it is actually a group of individual registers. The correct term for the registers in your processor is architeched registers. They are measured by the number of bits they can hold (e.g. 32 bit register). Most often now registers are an array of a semiconductor memory called Static Random Access Memory (SRAM).

Well those geniuses of engineering, the Germans that is, are at it again. Scientists at the University of Bonn set up an experimental quantum register. Rather ingeniously they first used one laser to hold five caesium atoms still by resting them in the trough of the light wave. Then they used a second laser to ‘write’ zeros on the qubits. Through the use of an extremely small and localized magnetic field the scientists were able to selectively influence the individual qubits. Then they used microwave radiation to ‘store’ all the quantum information on the qubits. By varying the strength of the magnetic field and thus the frequency of microwave radiation that the qubit would react to they were able to store the quantum information. That which is neither a 1 nor 0 but somewhere between the two.

Finally we learned in October of this year that a group of Perdue University physicists built a device that can somewhat effectively separate a stream of quantum objects, electrons in this case, according to their spin. It is actually a huge step as it has been quite a difficult problem to resolve. Kudos boys. I do urge you to read the entire article of this one as it contains much information that is clear and concise.